1. Field of the Invention
The present invention relates generally to chemical formulations used in semiconductor wafer fabrication and particularly to chemical formulations and methods to remove photoresist residues from semiconductor substrates following a resist plasma ashing step.
2. Description of the Prior Art
Semiconductor integrated circuits are produced by a process in which a photoresist is applied onto an inorganic substrate. Typically the fabrication of a photoresist involves the creation of a metalized layer having a patterned resist layer formed thereon. Initially, the pattern is formed on the photoresist by exposure to light and subsequent development and the formed pattern is then used as a mask. The portions of the inorganic substrate not masked by the pattern of the photoresist are etched by exposure to a metal etching plasma (such as a halogen based plasma) to remove exposed metal to form fine circuits. Then the photoresist is removed from the inorganic substrate by an etching step as described above. Next, a plasma ashing step is conducted (typically using an oxygen based plasma) in which the remaining resist is removed from the wafer. Finally, the remaining residue that is predominantly composed of inorganic compounds such as metal halides and metal oxides is removed from the inorganic substrate. The result is a patterned metalized layer.
Various chemical formulations are currently used to remove the inorganic compound residue. These formulations are generally holdovers from older semiconductor fabrication wet chemical resist removal processes that were used prior to the introduction of the resist plasma ashing technology. Typically, these prior art chemical formulations include strong reagents such as strong inorganic acids, strong bases and/or reactive amine containing compounds. However, such strong reagents can cause unwanted further removal of metal or insulator layers remaining on the wafer and are therefore undesirable in many instances. Additionally, strippers containing both amine component(s) and water may corrode metal, particularly copper, aluminum and aluminum-copper alloys.
Accordingly, it would be advantageous to provide improved chemical formulations to effectively remove residue following a resist ashing step that does not corrode and/or potentially degrade delicate structures which are meant to remain on a semiconductor wafer. Non-oxidizing acidic solvent solutions offer efficient residue removal and good compatibility with sensitive metals and dielectrics materials.